A vulnerability in the way Java 7 restricts the permissions of Java
applets could allow an attacker to execute arbitrary commands on a
vulnerable system.

Description

A vulnerability in the Java Security Manager allows a Java applet
to grant itself permission to execute arbitrary operating system
commands. An attacker could use social engineering techniques to
entice a user to visit a link to a web site hosting a malicious
applet.

Any web browser using the Java 7 Plug-in is affected.

Reports indicate this vulnerability is being actively exploited,
and exploit code is publicly available.

Impact

By convincing a user to load a malicious Java applet, an attacker
could execute arbitrary operating system commands on a vulnerable
system with the privileges of the Java Plug-in process.

....Mac systems with the Java 7 runtime are vulnerable. While there are no known attempts to use this vulnerability to specifically target Mac users, the exploit has been successfully triggered in both Safari and Firefox on Macs running Mountain Lion. Furthermore, the means to exploit this malware have been found distributed in underground malware development kits, making its easier for the exploit to be developed into malware by those wishing to target Mac users....

Early reports suggested that Google Chrome was immune to the problem, but that appears to have been a bug in the attacker's code. The Metaploit project released proof of concept code that exploits the flaw on all browsers and operating systems (Windows, OS X, Linux).

Code execution was confirmed with the latest Oracle and IBM Java 7 web browser plugin. IcedTea-Web using OpenJDK7 blocks this exploit by not allowing applet to change the SecurityManager (which is allowed in Oracle and IBM Java plugin).

I have been unable to perform the manual install, however. Do you think this patch will be eventually available from the repository?

In the meantime, does anyone know whether I should use the Linux RPM patch to update Java in Linux Mint 12 (KDE)?
I used the other one and I was unable to install the patch . I think I followed the instructions correctly, though.

The RPM is for RedHat based distros. Though you can use that on Debian based distros with alien, it is NOT recommended!!! Try the tar.gz file instead.

This patch will not be available in the repository, unless you have added a repository to install Oracle Java 7 from. The default repositories have OpenJDK Java 6 and 7 (which is not vulnerable), not Oracle Java 7 (as Oracle prohibits distribution of Oracle Java with operating systems).

That is a bit dramatic. The vulnerability is only for Oracle Java 7 in your browser, so just disable Oracle Java 7 in your browser. To a lesser extent /dev/urandom has a point there, because do you actually need Java in your browser? If you do, switch to OpenJDK and IcedTea and be rid of the vulnerability also.